Compound beam mechanical casing collar locator

ABSTRACT

A mechanical casing collar locator is disclosed. The casing collar locator has an outermost, locator leaf spring cage, and one or more radially stacked reinforcement leaf spring cages. Each leaf spring cage has a plurality of flexible leaf spring beam members, each having a locator dog thereon for engage collar recesses, or other recesses, in the wellbore casing. The leaf spring beam members of the reinforcement leaf spring cages radially support the leaf spring beam members and the locator dogs of the locator leaf spring cage for providing enhanced radially outward spring force.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 62/120,261, filed Feb. 24, 2015, the entirety ofwhich is incorporated herein by reference.

FIELD OF THE DISCLOSURE

Embodiments herein relate generally to apparatus and methods fordetection of casing collars in a casing string for positioning ofwellbore tools relative thereto, and in particular to a mechanicalcasing collar locator.

BACKGROUND

In the process of wellbore completion, a string of casing is typicallyrun into an open borehole and is cemented into place. Various downholecomponents can be located along the casing, including sleeve valves foraccess to a formation of interest. A downhole tool can be run into thecasing string on a conveyance string and the tool is located at specificdownhole components by feedback from a locater positioned on the tool.The locator detects the component itself, or another feature on thecasing, such as collars that can be spacially related to the position ofthe component. It is important that the tools are locatable at known anddesired locations within the casing for performance of well operations,including actuation of the downhole components in the string of casing.

In conventional embodiments, the casing comprises lengths or joints oftubing which are connected by threaded collars. Ends of the axiallyaligned joints of casing are threaded into the collars. Once threadedtherein, the ends of the casing do not abut, leaving an axial spacetherebetween. The axial space or recess formed in the collar has agreater radial dimension than a bore of the joints of casing, forming alocatable feature in the casing string. Alternatively, where casingconnections do not provide such a gap, specially designed locatortubulars or collars having a recess formed therein may be installed inthe casing string for the express purpose of location.

As is also known, locators can be used not only to detect the collar gapor recess, but can be used to locate any suitable recess or profile inthe string of casing, which may be formed at the downhole component,such as a sleeve valve. For example, a suitable profile can be formed atan end of a shifting sleeve movable therein.

A variety of apparatus are known to locate the collars within the casingstring to better understand the positioning of tools run into thewellbore relative to the casing component. Known casing collar locatorsinclude those using electronic or magnetic sensors in an attempt toconsistently locate the collars.

Other known locators are mechanical locators which comprise arrangementsof radially extending, biased members, including protruding dogs, whichreleasably engage a respective axial space along the casing string. Onceengaged in the collar or other recess, axial load or weight at surfaceon the downhole tool is resisted by the locater engagement in therecess, the shift in load or weight to the conveyance string beingobservable at surface as an indication of having reached the desiredlocation.

The reliability of location using mechanical locators is generallyrelated to the resolvable change in the force applied to the tool'sconveyance string during movement. When the locator engages a recess, acertain axial force is required to dislodge the locator therefrom. Ifthe locator engages the recess during a running in stage, an increaseddownhole force is required to dislodge it from the recess. If thelocator engages the recess during a pulling out of hole stage, anincreased uphole force is required to dislodge it from the recess. Theincreased force is measured by a change in the surface weight of theconveyance string. Typically, when running in using coiled tubing,lifting weight is used as a marker of locator positioning, and thus, thenature of the locator/recess interaction is designed for release of thelocater from the recess during pulling out. Others may use a reductionin weight or a pushing force and, in those instances, the nature of thelocator/recess interaction is designed for release of the locater fromthe recess during running in.

The release force is a function of a radially outward, recess-engagementforce and a ramping interface of the locator and recess interface. Therecess has uphole and downhole edges and the locator has leading andtrailing ramp surfaces. Pulling or pushing of the tool and locator formsaxial loading of the locator ramp against a recess edge. The interfaceimposes a radially inward release force on the locator, resisted by abiasing of the locator.

The mechanical advantage of a shallow or small interface angle produceslarge, radially inward force with small axial applications of weight,resulting in relatively indistinguishable weight change and poor locatorresolution. A steep or large interface angle produces a small radiallyinward force, even at large axial applications of weight, providingeasily detectable weight changes but at a risk of non-release of thelocator and a stuck tool and/or erratic performance.

For example, FIG. 1 is a portion of a cross-sectional view of aprior-art mechanical casing collar locator 10 with a locator dog 12located in a collar recess 14 formed by a collar 16 and adjacent casingjoints 18 and 20. The locator dog 12 is profiled, having an uphole rampor interface 22 and a downhole ramp or interface 24. The dog 12 istypically driven outward with a spring. The spring force, and ramp,determines the release behavior of the dog 12 from the recess 14.

As described above, the interface angle significantly affects theperformance of the casing collar locator. In this example, the upholeinterface 22 has an interface angle θ greater than 60 degrees withrespect to a direction 26 parallel to the axis of the casing 18.Consequently, the radial spring force Fs required to maintain thelocator dog in the recess is relatively small. However, a large upholeforce Fp is required to pull the locator dog 12 out of the recess 14.

It is believed that the release behavior or predictability of a locatordog having an interface angle greater than 60 degrees can become erraticdue to the requirement of a large release force for releasing thelocator dog out of the collar recess, even if the radial spring force issmall. As the interface angle becomes larger, even up to 90 degrees, thelocator dog becomes stuck.

At 60 degrees or smaller, release is much more predictable, however inorder to provide a visual indication at surface, the spring force mustbe quite high. Ideally, the interface and biasing force arecomplementary to provide sufficient weight change for consistentdetection of locator engagement, yet not so great as to risk toolentrapment or a non-consistent release force.

Given the risk of entrapment or poor detection resolution, there isstill room for improvement to locator technology.

SUMMARY

Given that tool entrapment is highly undesirable, the designed interfaceangles at the locator and recess are usually shallow and thereforerobust radial biasing is required to provide engagement indication.Biasing is typically associated with the spring material selection anddimensions. Given limited selections in material, the industry typicallyemploys larger springs for applying more force. Larger springs, coilsprings or spring beams, require a significant portion of the toolcross-section. If smaller robust springs are required, materialproperties need to be increased, however only at the risk of limitedelastic displacement before entering the plastic range of deformation.Further, springs such as coil springs are prone to trapping of debristherein which may affect tool performance.

In conventional downhole tools, the cross-section typically includesfluid passageways and apparatus, including equalization valves, slidingmembers and the like. Robust locators, having structure to provide highradial engagement biasing, can interfere with the sizing and placementof tool components and thus the strength of the biasing is generallylimited. Known prior art apparatus have such restricted diametricalarea, and the integration of a locator in such an environment limits thebiasing strength. Such restrictions can compromise the radial forceneeded to achieve a pull-through force which is high enough to beconsistently detected and ensure positive and reliable location. InCanadian Patent Application No. 2,693,676 to NCS Oilfield Services Inc.,the locator is physically positioned in the tool to reside within thesleeve valve, such as to engage ends of the tubular sleeve. The tool isfit with fluid passageways to conduct fluid across the tool, includingthrough the locator. A spring-loaded dog locator is provided having alocator body, dogs and coil springs between the dogs and the body forurging the dogs radially outwardly. The body structure occupies asignificant portion of the tool cross-section and thus, the springaspect is minimized, limiting the biasing force possible. Further, withrespect to published patent application CA 2,856,184 to NCS OilfieldServices Inc., a locator comprising a leaf spring cage having dog formedthereon is positioned concentrically about at least a J-slotarrangement. The J-slot arrangement occupies a significant portion ofthe tool cross-section and thus, the spring aspect is also minimized,limiting the biasing force possible.

Solutions to constraints on the spring can, to a certain extent, bemanaged with changes to spring material or spring thickness, however,this is also associated with reduced elastic range and potential forreduced fatigue life or even plastic deformation. Further, attempts tocounter reduced radial biasing forces by increasing the interface angleincreases the risk of tool entrapment or inconsistent release loads.

According to one aspect of this disclosure, there is provided anapparatus for locating an annular recess along a wellbore string. Theapparatus comprises: a plurality of circumferentially-spaced, radiallyoutwardly extending dogs for engaging the recess; and a plurality ofsupporting structures for supporting the plurality of dogs; wherein eachsupporting structure comprises: two or more radially stacked layers ofcircumferentially-spaced, radially flexible, leaf spring beam membersextending along an axial direction.

In some embodiments, each dog comprises a first interface for engagingan edge of the recess, the first interface being angled from the axialdirection at a first interface angle of about or less than 60 degrees.

In some embodiments, the first interface angle is about 50 degrees.

In some embodiments, the first interface is an uphole interface.

In some embodiments, at least a first layer of the two or more layers ofcircumferentially spaced leaf spring beam members form a locator cage.

In some embodiments, the locator cage is a slotted tubular.

In some embodiments, the circumferentially spaced leaf spring beammembers of the locator cage are supported at at least one of two axiallyopposite ends thereof by a solid tubular portion.

In some embodiments, the circumferentially spaced leaf spring beammembers of the locator cage are supported at each of two axiallyopposite ends thereof by a solid tubular portion.

In some embodiments, the at least first layer is the radially outmostlayer, and wherein at least a second layer of the two or more layers ofcircumferentially spaced leaf spring beam members form a reinforcementcage.

In some embodiments, the reinforcement cage is a slotted tubular.

In some embodiments, the circumferentially spaced leaf spring beammembers of the locator cage are supported at at least one of two axiallyopposite ends thereof by a solid tubular portion.

In some embodiments, the circumferentially spaced leaf spring beammembers of the locator cage are supported at each of two axiallyopposite ends thereof by a solid tubular portion.

In some embodiments, the reinforcement cage is concentrically receivedin the locator cage.

In some embodiments, each dog is supported by at least one beam memberof the first layer, and each beam member of the first layer is supportedby at least one beam member of the at least second layer.

In some embodiments, the locator cage further comprises a first couplingmechanism at an uphole end thereof for coupling the locator cage to afirst sub and a second coupling mechanism at a downhole end thereof forcoupling the locator cage to a second sub.

In some embodiments, after the locator cage is coupled to a first sub atthe uphole end thereof and to a second sub at the downhole thereof, theat least first reinforcement cage is axially fixed or axially moveablewithin a predefined range.

In some embodiments, the two or more radially stacked layers of leafspring beam members are radially aligned.

In some embodiments, the reinforcement cage is circumferentially fixedwith respect to the locator cage.

In some embodiments, the apparatus further comprises: a delimit pinextending from the reinforcement cage radially outwardly into a slotbetween two adjacent positioned in a slot between two adjacent springbeam members of the locator cage, for preventing the reinforcement cagefrom rotating with respect to the locator cage.

According to another aspect of this disclosure, there is provided anapparatus for locating an annular recess along a wellbore string. Theapparatus comprises: a tubular locator cage having a plurality ofcircumferentially-spaced, radially flexible, locator leaf spring beammembers extending along an axial direction, each locator leaf springbeam member having a locator dog thereon and extending radiallyoutwardly, the locator cage having a locator bore; and at least a firsttubular reinforcement cage fit concentrically within the locator bore,each of the at least a first tubular reinforcement cage having aplurality of circumferentially-spaced, radially flexible, reinforcementspring beam members extending along the axial direction and forsupporting the locator leaf spring beam members.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a portion of a cross-sectional view of a prior-art casingcollar locator having a dog thereon engaging a casing collar recess, thedog having an uphole interface with a relatively large interface anglegreater than 60 degrees, resulting in a requirement of a large upholepulling force to pull the dog from the recess, and resulting in risk oftrapping of the dog in the recess;

FIG. 2 is a perspective view of an assembled casing collar locator,according to an embodiment;

FIG. 3 is an end view of the casing collar locator of FIG. 1, showing anoutmost, locator leaf spring cage and two reinforcement leaf springcages being arranged concentrically;

FIG. 4 is a perspective view of a partially assembled casing collarlocator with the locator leaf spring cage and two reinforcement leafspring cages being axially offset, the leaf spring beam members of thelocator leaf spring cage and two reinforcement leaf spring cages beingaligned;

FIG. 5 is a perspective view of the locator leaf spring cage;

FIG. 6 is an end view of the locator leaf spring cage of FIG. 5;

FIG. 7 is a cross-sectional view of the locator leaf spring cage of FIG.5;

FIG. 8 is a perspective view of a reinforcement leaf spring cage;

FIG. 9 is a cross-sectional view of the reinforcement leaf spring cageof FIG. 8;

FIG. 10 is a cross-sectional view of the casing collar locator of FIG.1;

FIG. 11 is a portion of a cross-sectional view showing the casing collarlocator of FIG. 1 engaging a collar recess;

FIG. 12 is an enlarged view of portion A of FIG. 11, showing an upholeinterface of a dog engaging an uphole edge of the collar recess;

FIG. 13 is a perspective view of the locator leaf spring cage, accordingto some alternative embodiments;

FIG. 14 is a perspective view of a reinforcement leaf spring cage,according to some alternative embodiments; and

FIG. 15 is a perspective view of the locator leaf spring cage, accordingto some other embodiments.

DETAILED DESCRIPTION

Various embodiments of a mechanical casing collar locator are disclosedherein, comprising an outermost, locator leaf spring cage, and one ormore radially stacked reinforcement leaf spring cages. Each leaf springcage comprises a plurality of circumferentially-spaced, flexible, leafspring beam members. Each flexible leaf spring beam member of thelocator leaf spring cage comprises a locator dog formed to extendradially outwardly from an intermediate position thereof. Thereinforcement leaf spring cage radially supports the locator leaf springcage for providing enhanced radially outward spring force.

Each locator dog is a profiled dog, extending radially outwardly fromeach flexible leaf spring beam member of the locator leaf spring cage soas to engage collar recesses, or other recesses, in the wellbore casing.The profiling includes uphole and downhole interfaces or ramps, theselected angle of which is discussed below for adjusting pull-throughforces in combination with the recess.

The resulting casing collar locator provides significant radiallyoutward directed engagement force (i.e., a force of a directionperpendicular to and pointing away from an axis of the casing collarlocator), enabling a reduction in the interface angle of an engagementinterface of each of one or more profiled dogs, such that, the profileddogs of the casing collar locator can engage a collar recess with a lowrisk of tool entrapment and higher weight resolution at surface forconsistent detection of casing collar recesses. The casing collarlocator disclosed herein achieves high engagement force while able touse a minimum of the locator cross-section, or simply providesignificantly higher radial biasing forces while remaining within theelastic range of operation of the biasing with the radial range ofdisplacement required to enter and exit casing recesses.

In embodiments, the present locator achieves sufficient outwardlydirected radial force therein, such that an angle of an uphole interfaceor ramp of a profiled dog formed thereon is maintained at an angle belowthat at which erratic pull-through force could occur. In combination,the strong radial force and dog interface angle achieve an optimumpull-through force, such as about 3000-4000 dN, for positive, consistentand reliable location. The pull-through force can also be varied fromtool to tool, such as depending upon the number of spring cagesutilized.

Thus, in addition to the ability to provide suitable engagement forcewith low interface angles for restricted diametrical environments,further advantage is obtained where larger diametrical extent isavailable, and greater weight resolution can be achieved at surface. Thecasing collar locator disclosed herein is particularly useful for toolstrings which are arrange to position the locator therein away fromother internal apparatus so as to provide maximum diametric spacetherein. Generally, if the locator is used to locate a casing collarspaced axially from a shifting sleeve, rather than to the end of theshifting sleeve as known in the prior art, the locator can be spacedbelow other apparatus in the tool string where increased diametricalarea is available therein to accommodate the locator disclosed hereinand maximize the release resolution. Embodiments disclosed herein canlocate within a sleeve, however the sleeve length must be adjustedaccordingly.

Thus, the locator disclosed herein may be used in various scenarios. Forexample, in some embodiments, a downhole tool may comprise a bottom holeassembly (BHA) coupled to the locator disclosed herein. The locatorcomprises a bore forming a flow path, which is in fluid communicationwith a flow path of the BHA.

Turning now to FIGS. 2 to 4, a mechanical casing collar locator isshown, and is referenced using numeral 100. Similar to traditionalcasing collar locators, the collar locator 100 may be coupled to, ateither or both ends thereof, suitable subs 106 such as a crossover sub,and is used for locating one or more locator recesses of a casing stringsuch as at collar recesses 14. The one or more collar recesses 14 areformed as described above, and each collar recess has a recess diameter.

As shown, the collar locator 100 is a beam-type locator having a tubularlocator leaf spring cage 102 with a bore for receiving therein one ormore concentrically arranged, stacked reinforcement leaf spring cages104. FIG. 4 shows a partially assembled locator leaf spring cage 102 andtwo reinforcement leaf spring cages 104A and 104B, axially offset forbetter illustration.

As shown in FIGS. 5 to 7, in this embodiment, the locator leaf springcage 102 comprises a tubular housing 110 having a bore formedtherethrough. The housing 110 is machined to form a plurality ofcircumferentially and alternately arranged slots 108 and resilient, leafspring beam members 112 (denoted as locator leaf spring beam members112), extending along an axial or longitudinal direction. Therefore, thelocator leaf spring beam members 112 are spaced from each other, and areseparated by the slots 108.

Each leaf spring beam member 112 comprises a radially outwardlyextending dog 114 formed intermediate therealong. For example, in FIGS.5 to 7, eight (8) leaf spring beam members 112 are formed, each havingan integrated, radially outwardly extruded dog 114 located at about amid-point of the corresponding leaf spring beam member 112. The leafspring beam members 112 are made of metal material with suitableelasticity to provide required radial flexibility for dogs 114 to enterand exit the recess 14.

In this embodiment, each slot 108 terminates at an end 112A/112B spacedaxially inwardly from each opposing end of the housing 110, leaving arigid, solid tubular portion 118 at opposing ends of the locator leafspring cage 102. The tubular portion 118 supports the ends 112A and 112Bof each beam member 112, and provides a structure for retaining the beammembers 112 in axial and circumferential alignment.

In an unbiased position, the diameter about the dogs 114 is greater thanthat of the inside diameter of the casing, and corresponds more to adiameter of, or larger than that of, the circumferential collar recess.Accordingly, the dogs 114 drag along the casing string, biased to enterany recess therealong.

Referring to FIG. 7, the dog 114 of each leaf spring beam member 112 isprofiled, having an uphole locator ramp or interface 122 and a downholelocator ramp or interface 124. The interface angles α and β of thelocator interfaces 122 and 124, respectively, with respect to adirection parallel to the longitudinal axis of the locator leaf springcage 102 are chosen to be relatively small angles, depending on thedesign requirements. For example, in the embodiment shown in FIG. 7, thecasing collar locator 100 is used for locating collar recesses during apull-out-of-hole stage. Therefore, the downhole interface is angled suchthat the downhole tool including the casing collar locator 100 can bereadily run in and moved downhole along the casing and past the recessestherein. For example, the downhole interface angle β in this example isa relatively small angle such as about 15 degrees for ease of insertionof the locator into the casing. The uphole interface angle α may be anangle suitable for a sufficiently high resolution to locate a collarrecess with sufficient accuracy, e.g., about 60 degrees or smaller.

In this embodiment, the locator leaf spring cage 102 also has aplurality of screw holes 116 on each ends thereof for locking the casingcollar locator 100 to suitable subs (not shown).

To provide the radial range of motion, while maintaining the radiallyelastic deflection of the locator leaf spring cage 102, one or moreconcentrically arranged, stacked reinforcement spring cages 104 areprovided.

As shown in FIGS. 8 and 9, the structure of the reinforcement springcage 104 is similar to that of the locator leaf spring cage 102. Inparticular, the reinforcement spring cage 104 comprises a tubularhousing 130 having a bore formed therethrough. The housing 130 ismachined to form a plurality of circumferentially and alternatelyarranged slots 132 and resilient, leaf spring beam members 134 (denotedas reinforcement beam members 134), extending along a longitudinaldirection. At least the leaf spring beam members 134 are made of metalmaterial with suitable elasticity to provide required radialflexibility. However, in this embodiment the leaf spring beam members134 do not comprise any radially outward protrusion.

In this embodiment, the number of leaf spring beam members 134 of eachreinforcement spring cage 104 can correspond to that of the leaf springbeam members 112 of the locator leaf spring cage 102 such that eachlocator leaf spring beam member 112 is supported by at least onereinforcement beam member 134 to reinforcing the biasing thereof.

Similar to the slots 108 of the locator leaf spring cage 102, each ofthe slot 132 of the reinforcement spring cage 104 terminates spacedaxially inwardly from each opposing end of the housing 130, leaving arigid, solid tubular portion 138 at opposing ends of the reinforcementspring cage 104 for providing fixed supports at the end of each beammember 134 and a structure for retaining the beam members 134 in axialand circumferential alignment.

In this embodiment, each reinforcement spring cage 104 also comprises analignment port 136 axially spaced from a slot 132 for receiving analignment pin (described later).

The outer diameters of the reinforcement spring cages 104 are such thateach reinforcement spring cage 104 fits concentrically within the boreof an adjacent outer spring cage, which may be the locator leaf springcage 102 or an outer reinforcement spring cage 104.

In this embodiment, each reinforcement spring cage 104 has a lengthshorter than that of the locator leaf spring cage 102 to allow thelocator leaf spring cage 102 to receive other subs extending thereintofor coupling thereto.

As described above, a casing collar locator 100 may be assembled using alocator leaf spring cage 102 and one or more reinforcement spring cages104. In an example shown in FIGS. 2 to 4 and 10, a casing collar locator100 is assembled using a locator leaf spring cage 102. Concentricallyreceived within the locator cage 102 are two reinforcement spring cages104A and 104B, with the spring cage 104B received within the spring cage104A. As shown in FIG. 4, the spring cages 102, 104A and 104B arecircumferentially aligned such that the slots 108 and 132 thereof arealigned and the leaf spring beam members 112 and 134 are also aligned.

After the spring cages 102, 104A and 104B are axially in position (seeFIGS. 1 and 10), the alignment ports 136 of the reinforcement springcages 104A and 104B are also aligned. As the lengths of the tworeinforcement spring cages 104A and 104B are shorter than that of thelocator leaf spring cage 102, the alignment ports 136 thereof areexposed through a slot 108A of the locator leaf spring cage 102. Asshown in FIG. 1, a delimit pin 140, such as a socket head cap screw,extends through the slot 108 a and is secured into the alignment ports136 of the reinforcement spring cages 104A and 104B. The head of the pin140 projects from the cage 105A to be circumferentially constrainedwithin the slot 108A to prevent relative rotation between the springcages 102, 104A and 104B so as to maintain the radially stackedalignment of the leaf spring beam members 112 and 134.

As persons skilled in the art appreciate, the aligned slots 108 and 132in the concentric spring cages 102 and 104 can also provide fluidpathways therethrough, such as to a bore of the locator and tool string.Such fluid pathways are useful in flushing debris therethrough.

After assembling, the reinforcement spring cages 104A and 104B arecircumferentially constrained, but are allowed to move or slide axially.For ease of storage and transportation, the assembled casing collarlocator 100 may be capped at both ends thereof to prevent the inner,reinforcement spring cages 104A and 104B from moving out of the outer,locator spring cage 102.

As shown in FIG. 10, in use, the assembled casing collar locator 100 iscoupled to subs 106A and 106B on the uphole and downhole ends thereof.As shown, the outermost, locator leaf spring cage 102 comprises inwardlythreaded ends, operatively connected to outwardly threaded respectiveends of subs 106A and 106B. The connections of the locator leaf springcage 102 and subs 106A and 106B are further secured by the screws 142screwing through the holes 116 of the locator leaf spring cage 102 andonto the respective subs 106A and 106B. Of course, other known methodsof coupling the locator leaf spring cage 102 to subs 106A and 106B arealso readily available and may be alternatively used.

After coupling the locator leaf spring cage 102 to subs 106A and 106B,the reinforcement spring cages 104A and 104B are then axially sandwichedbetween the subs 106A and 106B, with the opposite ends of thereinforcement spring cages 104A and 104B loosely facing the butt ends ofsubs 106A and 106B. The axial location of the reinforcement spring cages104A and 104B is thus delimited by the subs 106A and 106B respectivelyat the uphole and downhole sides thereof.

As the spring cages 102, 104A and 104B have the same number of leafspring beam members 112, 134, and are aligned circumferentially, afterassembly, the leaf spring beam members 112, 134 of the spring cages 102,104A and 104B are radially aligned and stacked “on top of one another”.As will be described in more detail below, the stacked leaf spring beammembers 112, 134 provide higher radial spring force Fs for maintainingthe locator dogs 114 in the collar recess.

As described above, in a radially unbiased position, the diameter aboutthe dogs 114 is greater than that of the inside diameter of the casing.In some embodiments, the diameter about the dogs 114 is about, or evenlarger than, a diameter of the circumferential collar recess. Whilerunning in, each dog 114 and the corresponding leaf spring beam member112 are deflected radially inward to a smaller diameter, such as theinner diameter of the casing or the downhole component or sleeve. Anyaxial length change due to the radial deflection of the spring cage 102is reflected in a change in the axial spacing of the subs 106A and 106B.However, any change of axial length of the reinforcement cages 104A and104B are unconstrained as the delimit pin 140 can move axially in slot108A, and thus the reinforcement cages 104A and 104B can float axiallybetween subs 106A and 106B.

The inward, elastic deflection of the leaf spring beam member 112 of theoutmost locator leaf spring cage 102 urges and inwardly and elasticallydeflects the radially stacked, one or more leaf spring beam members 134of the one or more inner, reinforcement spring cages 104. As thecorresponding leaf spring beam members 112 and 134 are not mountedtogether, they can deflect radially and can shift axially with respectto each other. Comparing to the embodiment of a locator cage having“thick” leaf spring beam members but with no reinforcement cages, theabove design shown in FIG. 10 allows larger elastic range. Comparing tothe embodiment that the reinforcement cage(s) 104 are also axially fixedto the locator cage 102 (described later), the above design shown inFIG. 10 avoids stress caused by different deflections and/or differentlength changes of the leaf spring beam members 112 and 134.

As each leaf spring beam member 112 of locator leaf spring cage 102 iselastically supported radially by the respective leaf spring beammembers 134 of the one or more inner, reinforcement spring cages 104,the total radially outwardly directed spring force Fs is an aggregatedradial spring force exerted by the stacked leaf spring beam members 112and 134. For example, in the embodiment of FIG. 10, the casing collarlocator 100 comprises three spring cages 102, 104A and 104B, and theoutward radial force Fs is much larger than that of a single spring cage102, 104A or 104B. Those skilled in the art appreciate that an estimateor calculation of the radial force Fs is readily available using knowntheories.

When the dogs 114 move into a collar recess, the radially outward forceFs causes the dogs 114 and the leaf spring beam members 112 and 134 toreturn towards their normal, radially unbiased positions.

FIG. 11 is an illustration showing a portion of the casing collarlocator 100 being pulled uphole and having engaged a collar recess 14formed by a casing collar 16 between two adjacent casing joints 18 and20. The aggregated force Fs allows the casing collar locator 100 toprovide higher recess detection resolution (or weight resolution ifusing weigh change as an indication of detection) at surface.

As shown in FIGS. 11 and 12, when the tubing string and therefore thecasing collar locator 100 is again pulled uphole by an uphole force Fp,the edge 152 of the collar recess 14 pushes the uphole locator interface122 of the dog 114 engaged therewith, with a force Fr perpendicular tothe plane of the uphole locator interface 122. The force Fr correspondsto an axially downhole force Fd combatting the pulling force Fp, and aradially inward force Fi combatting the radially outward spring force Fsto urge the leaf spring beam members 112 and 134 to deflect radiallyinwardly against the combined or aggregated beam biasing.

As described above, the angle α of the uphole locator interface 122 isrelatively small, e.g., about or smaller than 60 degrees. However, byreinforcing the dog 114 with two or more leaf spring beam members 112and 134 to obtain an aggregated radial spring force Fs, a large force isthen required to pull the dog 114 out of the recess, giving rise to ahigher weight resolution at surface for recess detection.

Further, at about 60 degrees or less, risk of jamming between the upholelocator interface 122 and the edge 152 of the collar recess 14 and/ortool entrapment is minimized. In some embodiments, the uphole locatorinterface 122 may be angled at about 50 degrees. The degree of angle ofthe uphole locator interface 122 can be balanced with the number ofstacked spring cages 102 and 104 to provide the desired pull-throughforce to achieve reliable location. With the above described casingcollar locator 100, locating a collar recess 14 by the casing collarlocator 100 can be consistently observed at surface, and the profileddog 114 can also be reliably disengaged and removed from the recess 14.

As a comparison, the traditional mechanical casing collar locator 10 ofFIG. 1, assuming that it is manufactured using the same material as thecasing collar locator 100 disclosed herein, provides a smaller springforce Fs. Consequently, a large interface angle α, e.g., larger than 60degrees and up to 90 degrees, is needed to provide sufficient weightresolution at surface. However, such a large interface angle α has ahigh risk of jamming and/or entrapment.

In a process for locating a casing collar recess 14, the tool string,having the casing collar locator 100 positioned therein, is deployedinto the wellbore, such as on coiled tubing. The tool string is run intothe wellbore below a depth at which the operator anticipates a collar ofinterest to be located as is well understood in the art. The tubingstring is then lifted until the profiled dogs 114 reach the collarrecess 14 at which time the deflected, stacked spring cages 102 and 104are able to release and apply the radial outwardly force, resulting inpositive engagement of the profiled dogs 114 within the recess 14. Asthe dogs 114 engage in the recess 14, weight applied to the coiledtubing is transferred to the casing which can be observed at surface.When the tool string is to be moved within the wellbore, a pulling forceFp is applied to the coiled tubing string. At the design pull-throughforce, for example at about 3000-4000 daN (Decanewton), the profileddogs 114 are pulled out of the recess 14 and the tool can thereafter bemoved within the wellbore.

In some alternative embodiments, the collar recess 14 may also haveangled uphole and/or downhole edges, and the angles of the uphole and/ordownhole locator interface 122, 124 may be selected to mate the anglesof uphole and/or downhole edges, respectively.

In above embodiments, the uphole interface angle α is larger than thedownhole interface angle β. However, those skilled in the art appreciatethat the uphole and downhole angles α and β may be any suitable values.For example, in some alternative embodiments, the uphole and downholeinterfaces 122 and 124 have the same interface angle, i.e., α=β, and insome other embodiments, the uphole interface angle α may be smaller thanthe downhole interface angle β.

Referring again to FIGS. 7 and 10, in above embodiments, the leaf springbeam members 112 of the locator leaf spring cage 102 are also profiledat an inner surface thereof beneath the respective dogs 114, formingdiscontinuous areas or points of contact between the leaf spring beammembers 112 of the locator leaf spring cage 102 and the leaf spring beammembers 134A of the adjacent reinforcement leaf spring cage 104A.

In some alternative embodiments, the leaf spring beam members 112 of thelocator leaf spring cage 102 are not profiled at the inner surfacethereof (in other words, having a local, thicker cross-section at thedog location), and are in contact with the leaf spring beam members 134Aof the adjacent reinforcement leaf spring cage 104A substantially alongtheir entirety.

In some other embodiments, the leaf spring beam members 112 of thelocator leaf spring cage 102 are profiled at the inner surface thereof.Correspondingly, the leaf spring beam members 134A of the adjacentreinforcement leaf spring cage 104A are also profiled accordingly suchthat the leaf spring beam members 112 are in contact with correspondingleaf spring beam members 134A thereunder substantially along theirentirety.

In above embodiments, the leaf spring beam members 112 and 134 of thelocator leaf spring cage 102 and reinforcement leaf spring cage(s) 104,respectively, are supported at both ends 112A and 112B thereof.

In some alternative embodiments as shown in FIG. 13, the leaf springbeam members 112 may be supported only at one end 112A thereof by asolid tubular portion 118, being cantilevered therefrom. In suchcantilevered embodiments, additional spring force Fs may be requiredcompared to the above described embodiments to achieve the designpull-through force. Additional concentric reinforcement leaf springcages 104 or other types of springs may be added to increase the springforce.

Similarly in some alternative embodiments as shown in FIG. 14, the leafspring beam members 134 may be supported only at one end 134A thereof bya solid tubular portion 138, being cantilevered therefrom.

In some alternative embodiments as shown in FIG. 15, some leaf springbeam members 112-1 may be supported only at one end 112A thereof by asolid tubular portion 118A, being cantilevered therefrom, and other leafspring beam members 112-2 are supported at both ends 112A and 112Bthereof by solid tubular portions 118A and 118B, respectively.Similarly, in some alternative embodiments, some of the leaf spring beammembers 134 may be supported only at one end thereof by a solid tubularportion, being cantilevered therefrom, and others of the leaf springbeam members 134 are supported at both ends thereof by solid tubularportions, respectively.

In above embodiments, the leaf spring beam members 112 and 134 of thelocator leaf spring cage 102 and reinforcement leaf spring cage(s) 104,respectively, are radially aligned, and each of the leaf spring beammembers 112 and 134 (except those of the innermost reinforcement leafspring cage) is supported by one leaf spring beam member 134 thereunder.In some alternative embodiments, at least one of the leaf spring beammembers 112 and/or 134 is supported by two or more leaf spring beammembers 134 thereunder. For example, at least one reinforcement leafspring cage may be misaligned with the (locator or reinforcement) leafspring cage adjacent and radially outward thereof such that each leafspring beam member of the outer leaf spring cage is supported by twoleaf spring beam members of the inner leaf spring cage.

In above embodiments, each leaf spring cage comprises a same number ofleaf spring beam members. In some alternative embodiments, at least oneleaf spring cage comprises a different number of leaf spring beammembers.

In above embodiments, the leaf spring cages 102 and 104 arecircumferentially fixed to each other by a delimit pin 140. In somealternative embodiments, at least some of the leaf spring cages 102 and104 are not circumferentially fixed such that they may rotate andcircumferentially misaligned.

In above embodiments, each dog 114 is an integrated part of therespective leaf spring beam member 112 formed by outwardly extending amid-portion of the leaf spring beam member 112. In some alternativeembodiment, at least some dogs 114 are manufactured separately, and theneach dog 114 is mounted to an outer surface of the respective leafspring beam member 112 using suitable means such as welding, screwingand the like.

In above embodiments, the dogs 114 are at about a mid-point of theirrespective leaf spring beam members 112. In some alternativeembodiments, the dogs 114 are at a point axially offset from themid-point of the respective leaf spring beam members 112.

In some alternative embodiments, some leaf spring beam members 112 ofthe locator leaf spring cage 102 may not comprise any dogs.

In some alternative embodiments, the spring cages 102 and 104 are alsoaxially fixed to each other using suitable fastening means, e.g.,screws.

In the casing collar locator 100 disclosed herein, each dog 114 issupported by two or more leaf spring beam members 112 and 134, i.e.,directly supported by a locator leaf spring beam member 112 and furtherreinforced by one or more reinforcement leaf spring beam members 134. Inabove embodiments, the casing collar locator 100 comprises a locatorspring cage 102 for forming the locator leaf spring beam members 112,and one or more reinforcement spring cage 104 for forming thereinforcement leaf spring beam members 134.

In some alternative embodiments, the casing collar locator 100 comprisesa locator spring cage 102 for forming the locator leaf spring beammembers 112 for directly supporting the dogs 114. However, the casingcollar locator 100 does not comprise any reinforcement spring cage 104.Rather, one or more laminated, reinforcement leaf spring beams eachhaving one or more layers of leaf spring beam members 134 is coupled toeach locator leaf spring beam member 112 by using suitable fasteners.The reinforcement leaf spring beam may be circumferentially constrained,but may be allowed to move axially within a predefined range. Thelaminated, reinforcement leaf spring beams may be coupled to the innersurface, outer surface or both surfaces of the locator leaf spring beammember 112, as needed or desired.

In above embodiments, after the locator leaf spring cage 102 is coupledto a first and a second subs 106 at the uphole and downhole endsthereof, respectively, the reinforcement leaf spring cage(s) 104 areaxially fixed in a predefined position. In some alternative embodiments,after the locator leaf spring cage 102 is coupled to a first and asecond subs 106 at the uphole and downhole ends thereof, respectively,the reinforcement leaf spring cage(s) 104 may still be axially moveablewithin a predefined range.

Although embodiments have been described above with reference to theaccompanying drawings, those of skill in the art will appreciate thatvariations and modifications may be made without departing from thescope thereof as defined by the appended claims.

What is claimed is:
 1. An apparatus for locating an annular recess alonga wellbore string, comprising: a plurality of circumferentially-spaced,radially outwardly extending dogs for engaging the recess; and aplurality of supporting structures for supporting the plurality of dogs;wherein each supporting structure comprises: two or more radiallystacked layers of circumferentially-spaced, radially flexible, leafspring beam members extending along an axial direction.
 2. The apparatusof claim 1 wherein each dog comprises a first interface for engaging anedge of the recess, the first interface being angled from the axialdirection at a first interface angle of about or less than 60 degrees.3. The apparatus of claim 2 wherein the first interface angle is about50 degrees.
 4. The apparatus of claim 2 wherein the first interface isan uphole interface.
 5. The apparatus of claim 1 wherein at least afirst layer of the two or more layers of circumferentially spaced leafspring beam members form a locator cage.
 6. The apparatus of claim 5wherein the locator cage is a slotted tubular.
 7. The apparatus of claim5 wherein the circumferentially spaced leaf spring beam members of thelocator cage are supported at one of two axially opposite ends thereofby a solid tubular portion.
 8. The apparatus of claim 5 wherein thecircumferentially spaced leaf spring beam members of the locator cageare supported at each of two axially opposite ends thereof by a solidtubular portion.
 9. The apparatus of claim 5 wherein the at least firstlayer is the radially outmost layer, and wherein at least a second layerof the two or more layers of circumferentially spaced leaf spring beammembers form a reinforcement cage.
 10. The apparatus of claim 9 whereinthe reinforcement cage is a slotted tubular.
 11. The apparatus of claim9 wherein the circumferentially spaced leaf spring beam members of thelocator cage are supported at one of two axially opposite ends thereofby a solid tubular portion.
 12. The apparatus of claim 9 wherein thecircumferentially spaced leaf spring beam members of the locator cageare supported at each of two axially opposite ends thereof by a solidtubular portion.
 13. The apparatus of claim 9 wherein the reinforcementcage is concentrically received in the locator cage.
 14. The apparatusof claim 9 wherein each dog is supported by at least one beam member ofthe first layer, and each beam member of the first layer is supported byat least one beam member of the at least second layer.
 15. The apparatusof claim 9 wherein the locator cage further comprises a first couplingmechanism at an uphole end thereof for coupling the locator cage to afirst sub and a second coupling mechanism at a downhole end thereof forcoupling the locator cage to a second sub.
 16. The apparatus of claim 15wherein, after the locator cage is coupled to a first sub at the upholeend thereof and to a second sub at the downhole thereof, the at leastfirst reinforcement cage is axially fixed or axially moveable within apredefined range.
 17. The apparatus of claim 9 wherein the reinforcementcage is circumferentially fixed with respect to the locator cage. 18.The apparatus of claim 17 further comprising: a delimit pin extendingfrom the reinforcement cage radially outwardly into a slot between twoadjacent positioned in a slot between two adjacent spring beam membersof the locator cage, for preventing the reinforcement cage from rotatingwith respect to the locator cage.
 19. The apparatus of claim 1 whereinthe two or more radially stacked layers of leaf spring beam members areradially aligned.
 20. An apparatus for locating an annular recess alonga wellbore string, comprising: a tubular locator cage having a pluralityof circumferentially-spaced, radially flexible, locator leaf spring beammembers extending along an axial direction, each locator leaf springbeam member having a locator dog thereon and extending radiallyoutwardly, the locator cage having a locator bore; and at least a firsttubular reinforcement cage fit concentrically within the locator bore,each of the at least a first tubular reinforcement cage having aplurality of circumferentially-spaced, radially flexible, reinforcementspring beam members extending along the axial direction and forsupporting the locator leaf spring beam members.